The Reason Dead Batteries Bounce

For the last few years, very well-informed people have been able to tell if an alkaline battery is good or not simply by dropping them. When dropped from an inch or two above a hard surface, a good battery won’t bounce, and will sometimes land standing up. A dead battery, on the other hand, will bounce. Thanks to [Lee] and a few of his friends, we now know why this happens.

While hanging out with a few of his buddies, [Lee] was able to condense all the arguments on why dead batteries bounce to two theories. The first theory, the ‘bounce theory’ said dead batteries had an increase in outgassing in the battery, increasing the pressure in the battery, which increases the spring constant of the battery itself. The second theory, the ‘anti-bounce theory’, said the gel-like properties of the electrolyte worked as a sort of mass damper.

[Lee] designed an experiment to test the outgassing ‘bounce theory’ of bouncing batteries. Instead of dropping a battery, an object – in this case a brass slug – was dropped onto both good and bad batteries. There was no difference. Even after holes were drilled to vent any gasses inside the battery, the brass slug bounced off both good and bad batteries the same way.

This means the reason dead alkaline batteries bounce is due to the electrolyte. [Lee] cut open a few AA cells and found the electrolyte in a good battery was a mushy mess of chemicals. In the dead battery, this same electrolyte hardened into a solid mass. [Lee] compares this to an anti-bounce hammer.

Finally, more than a year after most of us learned about bouncing dead batteries thanks to [Dave Jones]’ video, we have an answer. It’s a chemical change in the electrolyte that turns it from a goo to a solid that makes dead batteries bounce.

23 thoughts on “The Reason Dead Batteries Bounce

  1. Indeed, it’s very well done! I like the scientific approach used here; first observe the phenomenon, construct hypotheses, design experiment to attempt to disprove the hypotheses, execute experiments, and draw conclusions.

    When I first heard about this, I assumed it was just another urban myth.

      1. I always wonder how can he talk that much. Most of his talk just repeating itself….

        In addition his voice is kind of annoying, I started listening as a podcast on my phone without image, and I always thought its a she.

  2. Neat, and nicely done !

    When it comes to dead blow hammers I’ve always thought, and actually find it more plausible that the dampening effect comes (mostly) from the fact that in a mass of round pellets,buckshot, etc act more like a high viscosity fluid ( pellets bouncing off each other, rather than molecules bouncing off each other in an actual fluid) and hence leads to a heavily inelastic collision, even though all constituting materials might still ( in isolation ) bounce very elastically off each other.

    1. Dead blow hammers do not rattle so that leads me to believe there is a viscous fluid in there with the shot. Probably a thick oil. I’ll let you know for sure when I finally split mine open here. The way it looks that could be any time now too.

  3. I wonder if this also explains the ‘clack’ test. I’ve found if I have have two dead AA’s in my hand and I clack them together they make a different sound to when they are fully charged. Good ones give a nice sharp clack where dead ones sound more metallic with a reverb like two metal spheres clacking together.

    1. Besides that one, a more conclusive test is to spin them, then briefly stop them and let go. The cooked egg will stop, but the spinning liquid in the raw egg will set it spinning again.

  4. Next development: battery under test stuck to a power piezo transducer, drive the transducer with a single pulse then observe the induced waveform to measure the status of the electrolyte.

    1. I was thinking the same when reading this. I seem to recall I read somewhere how a multiphase/freq pulse would be needed to test a gel/liquid vs solid. (Somehow I think it had to do with SONAR detectors in the WWII era, depended on salinity and temp of water) So say ten pulses at stepped freq’s would exhibit a change over most/all pulses if it was non solid, no change for any if it was a solid. I think it also had to do with testing non-Newtonian fluids. At certain freqs a pulse would show either solid/liquid as it changes it’s viscosity.

      Either way, pulsing a single freq shot or say half-dozen freqs would be negligible time difference. Now, do you read the wave propagation time delays or freq shift?

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